This invention relates to a process for forming solid particles. More specifically, the invention is directed to solid particles formed from a mixture of a crystallizable condensation homopolymer and a non-crystallizable condensation polymer, wherein at least of portion of the crystallizable condensation homopolymer of the solid particle is crystallized.
Polyethylene terephthalate (PET) is widely employed commercially in the fabrication of containers for liquids such as carbonated beverages. PET provides high strength and modulus with excellent toughness, thought to derive largely from its relatively high level of crystallinity, and the self-reinforcement achieved when it undergoes orientation in the blow molding process which is highly preferred for fabricating containers and to which PET is especially well-suited. However, in certain emerging market areas there is a need for improvements in the permeability of PET to carbon dioxide and oxygen. One such market area is that of carbonated beverage bottles smaller than one liter where the relatively large surface to volume ratio places greater demands on CO2 barrier properties. Another such market area is that of beer bottles where even a small amount of oxygen contamination will degrade the taste of the beer.
It has long been recognized in the art that polyethylene isophthalate (PEI), an amorphous polymer, provides considerable improvement in barrier properties over PET. However, because of its amorphous structure, PEI homopolymer has been found to be completely unsuited for use in container fabrication.
Among the improvements which have been disclosed in recent years is the incorporation of varying amounts of PEI into PET resins. The resulting PEI/PET resins have been found to have improved barrier properties over that of PET containers and, thus, have led to increases in the shelf life of many products. For oriented shaped articles requiring a longer shelf life, PEI has been used as a barrier layer in a multi-layer container or as a blend with PET in single-walled containers.
U.S. Pat. No. 4,403,090 to Smith discloses a method for making block copolyesters by separately forming isophthalic and non-isophthalic polyesters, melt blending the polyesters, and then polymerizing the melt blend in the solid state. Though detailed solid state polymerization conditions are provided, no specific methods beyond the foregoing are disclosed for making the block copolymers.
U.S. Pat. No. 4,643,925 to Smith et al. discloses a high molecular weight polyester resin prepared by solid state polymerizing a melt blend of PET and PEI homopolymers. Prepolymers of the component polymers having an inherent intrinsic viscosity (IV) of at least 0.3 dl/g are first melt blended, solidified into pellets or chips, crystallized, and then solid state polymerized at about 5xc2x0 C. to 20xc2x0 C. below the sticking temperature of the pellets.
U.S. Pat. No. 6,150,454 to Wu et al. discloses a copolyester composition made from a random copolymer of isophthalic and terephthalic acids, a nucleating agent, and a chain-branching agent. It is stated that the chain-branching agent is added to reduce the natural stretch ratio of the copolymer resins to about the stretch ratio levels of commercially available PET resins. The copolymers in Wu et al. are produced by combining the acids, glycols, branching agents, and nucleating agents in the melt and polymerizing to form the branched, random copolymers of patentees invention. Wu et al.""s disclosure is limited to up to 10% of IPA comonomer. It is well known in the art that the mechanical integrity of containers made of random TA/IA copolymers deteriorate rapidly with increasing amounts of the IA moiety above 10%.
The Japan Patent Application Publications H10-279784 and H11-322968 to Kawano disclose improved barrier properties using block copolymers formed from PEI and PET moieties. Kawano discloses melt blending PET with a copolymer of PET and PEI containing about 80% PEI to form block copolymers having up to 30% PEI.
U.S. Pat. Nos. 5,510,454, 5,540,868, 5,633,018, 5,714,262, and 5,730,913, hereby incorporated by reference, teach a method to make solid particles from a condensation polymer by a thermal shock crystallization process and subsequent polymerization of the crystallized polymer particles in the solid state to make high molecular weight polymer. In a process termed xe2x80x9cthermal shock crystallizationxe2x80x9d low molecular weight molten polymer droplets are deposited on a moving surface at a temperature corresponding to the maximum crystallization rate of the low molecular weight polymer, resulting in generation of crystals in an environment that highly favors crystal growth over nucleation which, in turn, results, in some cases, in unique crystalline morphology. The resulting low molecular weight polymer particles display an unusually high melting point thereby permitting solid state polymerization to be effected at higher temperatures than is possible using crystalline particles produced from conventional processes.
Because of the necessity to preserve the very high rates of crystallization required in the thermal shock crystallization process, the disclosures of U.S. Pat. Nos. 5,510,454, 5,540,868, 5,633,018, 5,714,262, and 5,730,913, are limited to copolymers having no more than 10 mol % of a comonomer.
James et al., Macromol. Chem. Phys. 2001, 202, no. 11, pp. 2267-2274 discloses an adaptation of the process of U.S. Pat. Nos. 5,510,454, 5,540,868, 5,633,018, 5,714,262, and 5,730,913 to form block copolymers from two crystalline oligomers, PET and polyethylene-2,6-naphthalate (PEN), having up to a 50/50 blend thereof.
U.S. Pat. No. 5,010,146 to Kohsaka et al. discloses random copolymers of a crystalline oligomer and an amorphous oligomer, PET and polycarbonate, formed by combining the oligomers in the melt followed by polymerization in the melt phase.
Not taught in the art is the feasibility of producing block copolymers of a crystalline oligomer and an amorphous oligomer having more than 10 mol % of the amorphous oligomer utilizing the method of U.S. Pat. Nos. 5,510,454, 5,540,868, 5,633,018, 5,714,262, and 5,730,913. In particular, not taught in the art is the preparation of a high molecular weight block copolymer of PET with greater than 10 mol % PEI employing the advantageous methods of thermal shock crystallization.
The present invention provides a process for forming solid particles. The process comprises the steps of: a) combining in molten form a major component of a crystallizable condensation homopolymer and a minor component of a non-crystallizable condensation polymer, wherein the crystallizable condensation homopolymer and the non-crystallizable condensation polymer each have a degree of polymerization of 2 to less than 48 prior to the combining; b) mixing the combined crystallizable condensation homopolymer and non-crystallizable condensation polymer in molten form to form a mixture that comprises 10 to 30 mol % of the non-crystallizable condensation polymer; c) forming the mixture into droplets; exposing the droplets to a thermal environment which results in the bulk of the droplet reaching within 15 seconds a temperature within xc2x110xc2x0 C. of the temperature at which the maximum rate of crystallization of the crystallizable condensation homopolymer occurs; and d) crystallizing at least a portion of the crystallizable condensation homopolymer in the mixture to form solid particles.
In one embodiment of the invention, the mixture comprises 15 to 25 mol % of the non-crystallizable condensation polymer.
In another embodiment of the invention, at least one of the crystallizable condensation homopolymer and the non-crystallizable condensation polymer has a degree of polymerization of 15 to 35.
Preferably, the mixture has a blockiness factor of at least 0.8, more preferably at least 0.9, most preferably at least 0.95.
In a preferred embodiment, the crystallizable condensation homopolymer is polyethylene terephthalate and/or the non-crystallizable condensation homopolymer is polyethylene isophthalate.
In one embodiment, the at least one polymer in the minor component of the mixture is not soluble in the major component.
In yet another embodiment, the minor component of the mixture can further comprise up to 20 mol % of one or more additional crystallizable condensation homopolymers or non-crystallizable condensation polymers.
In a further embodiment, the invention further comprises the step of solid state polymerizing the solid particles.